Methods and apparatus for rotation detection of a brushed DC motor

Abstract

Various embodiments of the present technology comprise a method and apparatus for rotation detection of a brushed DC motor. The method and apparatus may detect switching of the commutators and utilize signals indicative of switching to determine speed and/or rotation information of the motor. In one embodiment, the apparatus comprises an ADC, a difference circuit, an absolute value circuit, and a comparator connected in series with each other.

The invention claimed is: 
     
       1. A detection circuit connected to a brushed DC motor, comprising:
 a differential amplifier configured to detect a current of the brushed DC motor and generate an analog signal that is proportional to the current; 
 an analog-to-digital converter (ADC) connected to the differential amplifier and configured to convert the analog signal to a first digital signal; and 
 a digital circuit connected to the ADC and comprising:
 a difference circuit configured to:
 receive the first digital signal; and 
 compute a second digital signal, wherein the second digital signal is the difference of the first digital signal and a previous first digital signal; 
 
 an absolute value circuit connected to the difference circuit and configured to compute an absolute value of the second digital signal; and 
 a comparator circuit connected to the absolute value circuit and configured to:
 compare the computed absolute value with a predetermined threshold value; and 
 generate a comparator output according to the comparison. 
 
 
 
     
     
       2. The circuit according to  claim 1 , further comprising a reference voltage generator circuit connected to a non-inverting terminal of the differential amplifier and configured to generate a reference voltage. 
     
     
       3. The circuit according to  claim 2 , wherein the reference voltage generator circuit comprises:
 a first resistor connected in series with a second resistor; and 
 an operational amplifier connected to the first and second resistors. 
 
     
     
       4. The circuit according to  claim 1 , wherein the difference circuit further comprises a delay register configured to store the previous first digital signal. 
     
     
       5. The circuit according to  claim 1 , wherein the digital circuit further comprises a register connected to the comparator and configured to store the predetermined threshold value. 
     
     
       6. The circuit according to  claim 1 , further comprising a sense resistor comprising a first end and a second end; and wherein:
 the first end is connected to the brushed DC motor and an inverting terminal of the differential amplifier; and 
 the second end is connected to a non-inverting terminal of the differential amplifier and a ground. 
 
     
     
       7. The circuit according to  claim 1 , wherein the comparator circuit generates a HIGH comparator output if the computed absolute value is greater than the predetermined threshold value. 
     
     
       8. The circuit according to  claim 7 , wherein the comparator circuit generates a LOW comparator output if the computed absolute value is less than the predetermined threshold value. 
     
     
       9. The circuit according to  claim 7 , wherein the HIGH comparator output represents switching contact of a brush from one commutator to a different commutator. 
     
     
       10. The circuit according to  claim 1 , wherein the predetermined threshold value is selected according to a signal level indicative of switching of the brushed DC motor. 
     
     
       11. A method for detecting rotation information of a brushed DC motor having a plurality of commutators, comprising:
 detecting a current of the brushed DC motor; 
 generating an analog signal that is proportional to the detected current; 
 converting the analog signal to a first digital signal; 
 computing a second digital signal, wherein the second digital signal is a difference of the first digital signal and a previous first digital signal; 
 computing an absolute value of the second digital signal; 
 comparing the computed absolute value with a predetermined threshold value; and 
 generating an output according to the comparison, wherein the output represents switching from one commutator of the brushed DC motor to a different commutator. 
 
     
     
       12. The method according to  claim 11 , further comprising analyzing the output to determine a speed of the brushed DC motor. 
     
     
       13. The method according to  claim 11 , further comprising analyzing the output to determine a total number of rotations of the brushed DC motor during a time period. 
     
     
       14. A brushed DC motor system, comprising:
 a drive circuit; 
 a brushed DC motor connected to and controlled by the drive circuit, wherein the brushed DC motor comprises a plurality of commutators; 
 a detection circuit connected to the brushed DC motor and comprising:
 a differential amplifier configured to detect a current of the brushed DC motor and generate an analog signal that is proportional to the current; 
 an analog-to-digital converter (ADC) connected to the differential amplifier and configured to convert the analog signal to a first digital signal; 
 a difference circuit comprising:
 an arithmetic circuit configured to:
 receive the first digital signal; and 
 
 compute a second digital signal, wherein the second digital signal is the difference of the first digital signal and a previous first digital signal; 
 a register connected to the arithmetic circuit and configured to store the previous digital signal; 
 
 an absolute value circuit connected to the difference circuit and configured to compute an absolute value of the second digital signal; and 
 a comparator circuit connected to the absolute value circuit at a first terminal and configured to:
 compare the computed absolute value with a predetermined threshold value; and 
 generate a comparator output according to the comparison; and 
 
 
 a microcontroller connected to the detection circuit and configured to analyze the comparator output to determine at least one of:
 a speed of the brushed DC motor; and 
 a total number of rotations of the brushed DC motor during a time period. 
 
 
     
     
       15. The brushed DC motor system according to  claim 14 , wherein the comparator circuit generates a HIGH comparator output if the computed absolute value is greater than the predetermined threshold value. 
     
     
       16. The brushed DC motor system according to  claim 15 , wherein the comparator circuit generates a LOW comparator output if the computed absolute value is less than the predetermined threshold value. 
     
     
       17. The brushed DC motor system according to  claim 15 , wherein the HIGH comparator output represents switching contact of a brush from a first commutator from the plurality of commutators to a second commutator from the plurality of commutators. 
     
     
       18. The brushed DC motor system according to  claim 14 , further comprising a reference voltage generator circuit connected to a non-inverting terminal of the differential amplifier and comprising:
 a first resistor connected in series with a second resistor; and 
 an operational amplifier connected to the first and second resistors. 
 
     
     
       19. The brushed DC motor system according to  claim 14 , wherein the predetermined threshold value is selected according to a signal level indicative of switching of the brushed DC motor. 
     
     
       20. The brushed DC motor system according to  claim 14 , wherein the microcontroller is further connected to the drive circuit and configured to supply a feedback signal to the drive circuit, wherein the feedback signal controls at least one of: a speed and a direction of rotation of the brushed DC motor.